He does look like a cuckoo Marans. Regular silver based, not golden.
golden cuckoos are made just like any other variety. You breed two cuckoo Marans to each other, and the offspring is the same breed as the parent. If the parents are different breeds, or different color varieties of the same breed, the offspring are going to be mixed color or mixed breed.
I think you could eventually get to a golden cuckoo by this start, depending on who the momma of the chicks are. But, it would take several generations of back crossing to get the correct color, type and egg color. It won't be a one time deal.